Froth flotation is a commonly employed process for concentrating minerals from ores. In a flotation process, the ore is crushed and wet ground to obtain a pulp. A frothing agent, usually employed with a collecting agent, is added to the ore to assist in separating valuable minerals from the undesired or gangue portions of the ore in subsequent flotation steps. The pulp is then aerated to produce a froth at the surface thereof and the collector assists the frothing agent in separating the mineral values from the ore by causing the mineral values to adhere to the bubbles formed during this aeration step. The adherence of the mineral values is selectively accomplished so that the portion of the ore not containing mineral values does not adhere to the bubbles. The mineral-bearing froth is collected and further processed to obtain the desired minerals. That portion of the ore which is not carried over with the froth, usually identified as "flotation tailings", is usually not further processed for extraction of mineral values therefrom. The froth flotation process is applicable to ores containing metallic and non-metallic mineral values.
In flotation processes, it is desirable to recover as much mineral values as possible from the ore while effecting the recovery in a selective manner, that is, without carrying over undesirable portions of the ore in the froth.
While a large number of compounds have foam or froth producing properties, frothers widely used in commercial froth flotation operations include polyalkylene glycol compositions and alkyl ethers thereof (see, for example, U.S. Pat. Nos. 3,595,390, 2,611,485 and 2,695,101). The frothers most widely used in froth flotation operations are compounds containing a non-polar, water-repellant group and a single, polar, water-avid group such as hydroxyl (OH). Typical of this class of frothers are mixed amyl alcohols, methylisobutyl carbinol (MIBC), hexyl and heptyl alcohols, cresols, terpinol, etc. Other effective frothers used commercially are the C.sub.1 -C.sub.4 alkyl ethers of polypropylene glycol, especially the methyl ether and the polypropylene glycols of 140-2100 molecular weight and particularly those in the 400-1100 range.
Although mineral recovery improvements from a preferred frother in the treatment of an ore can be as low as only about 1 percent over other frothers, this small improvement is of great importance economically since commercial operations often handle as much as 50,000 tons of ore daily. With the high throughput rates normally encountered in commercial flotation processes, relatively small improvements in the rate of mineral recovery result in the recovery of additional tons of minerals daily. Obviously, any frother which promotes improved mineral recovery, even though small, is very desirable and can be advantageous in commercial flotation operations, especially in view of increasing energy costs.
It is an object of the present invention to provide frothing agents which improve the selective recovery of mineral values from ores. Further, it is an object of the present invention to provide frothing agents which can be satisfactorily employed in present flotation processes. Further objects of the present invention will become evident in view of the details set forth hereinbelow.
In accordance with the present invention, it has been found that, in a process for collecting mineral values from an ore which comprises mixing ground ore with water to form an ore pulp, aerating said pulp in the presence of a frother agent, improved recovery results are obtained with mercaptan polyalkylene oxide compositions (hereinafter referred to as "mercaptan frothers") of the general formula: EQU R [S(EO).sub.x (PO).sub.y (BO).sub.z H].sub.n
wherein, in said formula,
Eo = c.sub.2 h.sub.4 o, po = c.sub.3 h.sub.6 o and BO = C.sub.4 H.sub.8 O, PA1 n = 1 or 2, PA1 x = 0-4, PA1 y = 1-10, PA1 z = 0-2, PA1 the average sum of the x, y and z groups is from 2 to about 12, PA1 R represents alkenyl of 3-5 carbon atoms, an alkyl group of from 1 to about 8 carbon atoms or an aryl group, and PA1 the average sum of all x+y+z groups is from 2 to about 12, PA1 R represents a bridging --(CH.sub.2).sub.m --radical wherein m = 1-6, or a bridging benzylidene radical ##STR1## or mixtures of the above.
and where n = 1,
where n = 2
As used herein, the term "average sum" means the average number of EO, PO or BO groups per molecule in a given composition or mixture of compositions and also includes mixtures of compositions having varying amounts of the same alkylene oxide group such as, for example, a product mixture of frother compositions RS(PO).sub.3 H, RS(PO).sub.5 H and RS(PO).sub.7 H wherein the average sum of PO groups per molecule in the product mixture is 5. The average sum of alkylene oxide groups present in a given mixture can readily be determined according to conventional procedures.
The pure compositions as such are useful in the method of the present invention although the reaction mixtures or mixed fractions are desirably utilized as these are effective and can be utilized without additional costly purification steps. The PO reactants (C.sub.3 H.sub.6 O) include 1,2- and 1,3-propylene oxide while the BO reactants (C.sub.4 H.sub.8 O) are meant to include only 1,2- and 2,3-butylene oxide.
As used herein, the term "alkyl" means and includes straight- or branched-chain radicals such as, for example, methyl, ethyl, isopropyl, butyl, t-butyl, pentyl, n-hexyl, isohexyl, heptyl, octyl, isooctyl and the like. The term "aryl" as used herein means, for example, phenyl, benzyl, and substituted phenyl radicals derived from, for example, toluene, ethyl, benzene, cumene, xylene, t-butyl benzene and the like. Likewise, the benzyl radicals can bear various substituents which do not affect the basic frother properties of the compositions. The term "alkenyl" includes the known propene, butene and pentene radicals.
Mixtures of compostions of the above formula are preferred for use in the present invention. Compositions of the above formula wherein n is 1 also constitute a preferred class herein. In another preferred class of frothers, n is 2. Compositions wherein n is 1 and R is alkyl or R is propenyl, constitute other preferred classes. In another preferred embodiment n is 1, z is 0 and the sum of x+y is from 2 to about 8. In another embodiment, mixtures of compositions wherein n is 1, z is 0 and the average sum of x+y is from about 2 to about 8 are preferred. Mixtures of the foregoing embodiment wherein R is also alkyl of 1 to about 6 carbon atoms comprise a further preferred class. Mixtures of compositions wherein n is 1, z is 0, the average sum of x+y is from 2 to about 8 and R is methyl are also preferred. In a further embodiment, mixtures of compositions wherein n is 1, x and z are each 0, the average sum of y is from 2 to about 8 and R is alkyl of 1 to about 6 carbon atoms are preferred. Mixtures of compositions wherein x and z are each 0 and the average sum of y is 5 or 7, respectively, constitute other preferred embodiments. Mixtures of compositions wherein n is 1, x and z are each 0, the average sum of y is 5 or 7, respectively, and R is alkyl of from 1 to about 6 carbon atoms are particularly preferred. In additional embodiments wherein n is 2 the following mixtures of compositions are also preferred: (a) z is 0, R is -- CH.sub.2--.sub.m and m is from 1 to about 4; (b) z is 0, x is 0 and m is 1-4; (c) z is 0, the average sum of all x+y groups is 2 to about 8 and m is 2-4; (d) R is a benzylidene radical, and (e) z is zero, R is a benzylidene radical, and the average sum of all x+y groups per molecule is from 2 to about 8.
The frothers of the present invention are added to the ore and intimately mixed therewith either alone or together with a collector prior to and/or during the flotation step. The ore pulp-frother mixture is then treated under conditions to form a froth. The froth selectively removes the mineral values from the ore and the mineral-rich froth is separated from the ore flotation pulp and recovered. This value-depleted pulp which remains in the flotation cell is removed. The mineral-rich froth is then further treated to recover the desired mineral values. In accordance with the process of this invention it has been found that both the amount of mineral values which are recovered and the concentration of mineral values in the froth are substantially increased over prior processes which employ known frothers. These processing improvements are obtained with substantially the same or lower quantities of frothing agents as compared to those used currently in flotation operations. Accordingly, the present invention provides substantial advantages over prior processes.
The frothers of this invention can be employed in the flotation of metallic and non-metallic ores. Exemplary ores which are processed include sulfides and oxides of copper, molybdenum, lead, zinc, iron, nickel, cobalt, and the like. Such ores may also contain precious metal values. Other exemplary ores are phosphate rock, cement rock, glass sands, feldspars, fluorspars, micas, clays, talcs, coals and ores containing tungsten, manganese, sulfur, and water-soluble minerals such as sodium and potassium chlorides, and the like. The frothers of this invention are employed in amounts of from about 0.005 lbs. per ton ore to about 0.5 lb. per ton of ore; or preferably from about 0.01 lb. per ton ore to about 0.1 lb. per ton ore. Those skilled in the art will recognize that frother amounts will vary depending upon a given plant operation, ore type, etc., and that the optimum amount will be determined by mill trial runs. Preferably, the frothers are employed in the recovery of copper of molybdenum, preferably molybdenum.
The frothers of the present invention are prepared by methods known to the art, including block polymer preparation methods.
The frothers may be prepared by reacting an appropriate mercaptan of the formula RSH, where n is 1, or R(SH).sub.2 where n is 2, wherein R is as hereinabove defined, with an alkylene oxide (e.g., ethylene-, propylene- or butylene-oxide) or mixtures thereof. The greater the quantity of the alkylene oxide used, the longer the chain length and the higher the molecular weight of the mercaptan frother obtained. The mercaptan reactants utilized to prepare the mercaptan frother agents are known in the art and can be readily obtained or prepared by known methods by those skilled in the art. Typical of such mercaptan agents are, for example, methanethiol, 1,2-ethanedithiol, 1-butanethiol, 2-butanethiol, thiophenol, benzyl mercaptan, toluenethiol, 4-t-butylthiophenol, 1,6-dithiolhexane, 2-methyl-2-propanethiol, 1,2-propanedithiol, propenethiol and the like. Also, allyl alcohol can be reacted with a mercaptan RSH in the presence of UV light to give RS(CH.sub.2).sub.3 OH, which can then be further reacted with EO, PO or BO reactants to obtain the product desired.
The preparation of the frothers of the present invention is effected in the presence of a catalyst such as alkalies, e.g., sodium or potassium hydroxide. The reaction may be carried out sequentially with either the EO, PO or BO being added first or concurrently where two or more oxides are reacted as a mixture. Reaction temperatures up to about 150.degree. C. to about 225.degree. C. may be employed and pressures up to 1000 pounds or more per square inch may be used.
The mercaptan frothers useful in the present invention may be characterized in terms of their molecular weights. Products of molecular weight in the range of from about 150 to about 1000 are suitable for use as frothers with the range of about 200 to about 600 being preferred.
The quantities of reactants are adjusted so that a frother of desired molecular weight may be obtained. For example, a molar quantity of the mercaptan reactant is reacted with sufficient amounts of EO, PO or BO, either separately or in combination with one or both other oxides, so that the final polymeric condensate, in either block or random form, is of the molecular weight range desired. The amounts of EO, PO and BO necessary to achieve the various compositions within the above-defined formula will be readily apparent to those skilled in the art, who will also recognize that the chain length is based on an average determination of EO, PO and BO groups present.
The frothers of this invention can be employed either alone or in conjunction with standard frothers and with a conditioning agent or modifier and/or a water-soluble or oily collector or promoter. Suitable water-soluble collectors or promoters which can be employed in the flotation of sulfide or oxide metallic ores are alkali metal xanthates, sodium or potassium ethyl, isopropyl, secondary or isobutyl, amyl, or isoamyl and hexyl xanthates, alkyl thiols, and dithiophosphates such as dicresyl, diethyl, diisopropyl, disecondary or diisobutyl, diamyl or diisoamyl and dihexyl dithiophosphates as free acids or as sodium, potassium or ammonium salts, as well as mercaptobenzothiazole derivatives. Representative oily collectors which can be employed with the frothers of this invention include dithiocarbamates such as S-allyl-N-ethyldithiocarbamate, S-allyl-N-isopropyldithiocarbamate and S-allyl-N-methyl-dithiocarbamate, as well as allyl xanthates, dialkl thionocarbamates and (alkoxycarbonyl) alkylxanthates; these collectors are oil-soluble.
In the flotation of non-metallic ores, suitable water-soluble and oil-soluble collectors or promoters are oleic acid, crude and refined tall oil, and tall oil fatty acids, naphthenic acids, the sodium, potassium, and ammonium soaps of such acids, black liquor soap, petroleum sulfonates, organic phosphates and polyphosphates, sulfonated oils and fatty acids, sulfosuccinates and sulfosuccinamates. Cationic type collectors such as long chain amines or imidazolines are employed in the flotation of silica and silicates and water-soluble minerals.
Depending on the type of ore treated, conditioning or modifying agents such as alkalies and acids to adjust pH so as to improve selectivity, flotation depressants to inhibit the flotation of unwanted minerals, and activators to enhance flotability and improve flotation rates may be used with the frothers of this invention.